I think folks are getting two topologies and implementations confused. The ML BalancedForce® Alignment takes 2 opposed drivers "spaced 180 degrees apart" in a sealed relatively small cabinet and as such, the back waves essentially cancel out.
Ok, I see the source of your confusion. "Spaced" 180 is not "wired" 180, aka opposite polarity. That would be a box dipole, no such thing exists to my knowledge. Regardless, its incorrect. The ML is a force cancelling design, the drivers are IN phase.
That's precisely what Alan demonstrated with the nickel. The chassis attachment means ZERO, the forces are cancelled regardless...by the "spaced 180" drivers. The ONLY thing the connected chassis does is stiffen the enclosure. It is,
as demonstrated , completely irrelevant to force cancelling.
A) Are the drivers physically attached in any other company other than Vivid Audio and KEF? No.
You have no idea. The 80s Pioneer paper showed...interconnected drivers.
Regardless, its irrelevant to the topic - Force cancellation. Its not a necessity whatsoever.
B) Is there a difference between "cancelling" 2 drivers' rear wave via installing in a sealed cabinet
That is all your misunderstanding of "spaced".
They are different design topologies with different end results that are somewhat related.
And the Vivid Audio / KEF implementation cancels the secondary force from the cones (resultant in the driver chassis) while the ML / Pinnacle cancels the primary force from the actual cones. Makes sense?
They all do the exact same thing. Force cancel. The only difference is the added structural stiffening of interconnected opposed drivers. Unnecessary for force cancellation, as DEMO'd. Also unnecessary in a small sub cube type enclosure.
In a larger sidewall floor standing type design (Giya, KEF blade, etc), there would be possibly beneficial added stiffness.
Bottom line, force cancellation is nothing new.